Expounds on two things I've seen confuse inexperienced users:
transactions/outputs in
gettxoutsetinfo: a user thought this was the total number of transactions or outputs ever seen on the chain, whereas it's only the number in the UTXO.bestblock in
gettxout: a user thought this was the block that included the output, not realizing it was the tip of the current best block chain. I also copied this text togettxoutsetinfofor congruency. I skimmed other uses of "bestblock" in the RPC docs and they seemed clear to me.